CHF is recognized as one of the most common causes of hospitalization and mortality in Western society, and has a great impact on the quality of life. CHF is a disorder characterized by low systemic perfusion and inefficient cardiac function. CHF causes may include myocardial insult due to ischemia, cardiomyopathy and other processes. Pathophysiologic mechanisms that are directly associated with CHF include reduced cardiac output, increase in cardiac filling pressures, and fluid accumulation, which may lead to, for example, pulmonar congestion and dyspnea. Impairment of systolic function may result in poor left ventricular contraction and reduced cardiac output, which may generate clinical symptoms including effort intolerance, dyspnea, reduced longevity, edema (lung or peripheral) and pain. A patient with systolic dysfunction may usually have a larger left ventricle because of phenomena called cardiac remodeling aimed to maintain adequate stroke-volume. This pathophisiologic mechanism is associated with increased atrial pressure and left ventricular filling pressure. With abnormal diastolic function, the left ventricle may be stiff and markedly less compliant partly because of abnormal relaxation leading to inadequate cardiac filling at normal pressures. Maintenance of adequate cardiac filling at higher filling pressures may be needed to maintain cardiac output. This mandatory rise of filling pressure to maintain cardiac filling and output may lead to pulmonary venous hypertension and lung edema.
Presently available treatments for CHF fall into three generally categories: (1) pharmacological, e.g., diuretics; (2) assist systems, e.g., pumps; and (3) surgical treatments. With respect to pharmacological treatments, vasodilators have been used to reduce the workload of the heart by reducing systemic vascular resistance and diuretics to prevent fluid accumulation and edema formation, and reduce cardiac filling pressure.
Assist devices used to treat CHF may include, for example, mechanical pumps. Mechanical pumps reduce the load on the heart by performing all or part of the pumping function normally done by the heart. Currently, mechanical pumps are used, for example, to sustain the patient while a donor heart for transplantation becomes available for the patient. There are also a number of pacing devices used to treat CHF. Resysnchronization pacemakers have also been used to treat CHF. Finally, there are at least three extremely invasive and complex surgical procedures for treatment of heart failure: 1) heart transplant; 2) dynamic cardiomyoplasty; and 3) the Batista partial left ventriculectomy.
In extreme acute situations, temporary assist devices and intraaortic balloons may be helpful. Cardiac transplantation and chronic left ventricular assist device (LVAD) implants may often be used as last resort. However, all the assist devices currently used are intended to improve pumping capacity of the heart and increase cardiac output to levels compatible with normal life, reducing filling pressures and/or preventing edema formation. Finally, cardiac transplantation may be used to treat extreme cardiac dysfunction cases, however this procedure is highly invasive and is limited by the availability of donor hearts. The mechanical devices may allow propulsion of significant amount of blood (liters/min) and this is also their main limitation. The need for power supply, relatively large pumps and possibility of hemolysis and infection are all of concern.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.